Underground Explosions Carve Twin Craters on Mars

Dramatic explosions deep under the Mars surface, possibly involving ice, are believed to have created a pair of massive craters spotted side-by-side in satellite images taken in January by the European Space Agency.

What makes the twin craters remarkable is the central pit found in each, which indicate the presence of water on or just below the surface of the red planet.

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In a report on the craters published on April 11, ESA scientists proposed a range of theories on what caused them.

"When an asteroid hits the rocky surface of the planet, both it and the surface are compressed to high densities," scientists with the ESA reported last week. "Immediately after the impact, the compressed regions rapidly de-pressurize, exploding violently."

The crater pits may form when the ice or rock in a meteor melts after impact, draining away through fissures in the crater. Another theory researchers proposed is that ice just under the surface rapidly heats up on impact, and vaporizes in an explosion immediately after.

Both craters lie in Mars' Thaumasia Planum region, a wide plateau just south of Valles Marineris, a canyon that's been called "the largest canyon in the solar system."

Though the two craters -- which measure more than 30 miles across each -- are side by side, the crater pits at the center of each differ greatly in size.

"Compared to the Arima crater, perhaps more subsurface ice was present and more readily vaporized in the southern crater, punching through slightly thinner crust to leave a larger pit," the report adds.